1. Field of the Invention
The present invention relates to a high frequency resonator and a manufacturing method therefor. More specifically, the present invention relates to a ceramic resonator and a manufacturing method therefor, in which a plurality of interconnected electrodes are formed on a face of a sub-wafer by printing a metal paste, and a plurality of the electrodes are also printed on the other face of the sub-wafer so that uniform capacitances can be obtained from the both end portions of the capacitor chip, thereby improving the characteristics of the resonator.
2. Description of the Prior Art
Generally, the ceramic resonators which periodically oscillate by being tuned with a certain frequency are widely used as oscillators in remote controllers, floppy disc drivers (FDD), hard disc drivers (HDD), watches and the like. The high frequency resonators include 2-terminal type and 3-terminal type. In the 2-terminal type, a capacitor is externally attached to the resonator, while in the 3-terminal type, the capacitor is internally installed. FIG. 1 illustrates a 3-terminal type resonator.
As shown in FIG. 1, a resonator 10 includes: a piezoelectric device 13, a capacitor 11, and a lead frame 15 for receiving the piezoelectric device 13 and the capacitor chip 11. FIG. 2 is a detailed illustration of the capacitor chip 11 which is internally installed in the resonator of FIG. 1. This capacitor is manufactured by going through the process as shown in FIGS. 3(a)-3(e).
That is, the manufacturing process for the capacitor chip according to the present invention is carried out as shown in FIG. 3. That is, as shown in FIGS. 3a and 3b, a wafer is cut into a plurality of sub-wafers 1, and then, an electrode layer 2 is formed on one face of the sub-wafer 1. Then an electrode layer 4 is formed on the other face of the sub-wafer 1 in the same manner. Then as shown in FIG. 3c, a resist layer 3 is formed by printing a photo-imageable resist on a part of the electrode layer 2 of the sub-wafer 1. Then the sub-wafer 1 is exposed by using a pattern film, and then, the resist is removed by carrying out an etching on the areas other than the exposed areas, so as to form an electrode 2a as shown in FIG. 3d. Meanwhile, for an impedance matching, another electrode 4a is formed on the other face of the sub-wafer 1. After forming the electrodes, the sub-wafer 1 is cut in the xxe2x80x94y direction as shown in FIG. 3d, and thus, a capacitor chip 11 is obtained as shown in FIGS. 2 and 3e. 
However, in the capacitor chip manufacturing method employing the above described lithographic process, the shapes of the electrodes of the both faces of the sub-wafer are different from each other. Therefore, the matching between the both face electrodes becomes difficult, and therefore, the manufacturing process becomes complicated. Further, the capacitances of the both ends become different from each other, and therefore, the resonator characteristics are ultimately affected adversely.
The present invention is intended to overcome the above described disadvantages of the conventional technique.
Therefore it is an object of the present invention to provide a ceramic resonator in which a capacitor of the resonator is manufactured by a simple process, and uniform capacitances can be obtained from the both end portions of the capacitor, thereby improving the characteristics of the resonator.
It is another object of the present invention to provide a method for manufacturing a ceramic resonator in which a capacitor of the resonator is manufactured by a simple process, and uniform capacitances can be obtained from the both end portions of the capacitor, thereby improving the reliability of the resonator.
In achieving the above objects, the high frequency resonator according to the present invention includes: a ceramic piezoelectric device; a capacitor; a lead frame for securing the ceramic piezoelectric device and the capacitor; and an epoxy resin molding film for molding the piezoelectric device, the capacitor and the lead frame into a unitized form. The high frequency resonator further includes: an electrode part formed by printing a metal paste on one face of a sub-wafer of a capacitor chip in a dual-striped form; and another electrode part formed by printing a metal paste on another face of the sub-wafer so as to be partly overlapped with the electrode part of the one face of the sub-wafer.
In another aspect of the present invention, the method for manufacturing a ceramic resonator according to the present invention includes the steps of: forming a ceramic piezoelectric device, a capacitor chip and a lead frame; assembling the piezoelectric device and the capacitor chip into the lead frame; and molding the assembled chip by using epoxy resin. The process for making the capacitor includes the steps of: cutting a ceramic wafer into a plurality of sub-wafers; printing electrodes on one face of the sub-wafer in a dual-striped form, drying the sub-wafer thus printed; printing another electrode on a central part of another face of the sub-wafer so as to be overlapped with the electrodes of the one face of the sub-wafer; drying the sub-wafer thus printed; baking the sub-wafer thus dried; and cutting the sub-wafer thus baked into a plurality of capacitors.
In still another aspect of the present invention, the high frequency resonator according to the present invention includes: a ceramic piezoelectric device; a capacitor; a lead frame for securing the ceramic piezoelectric device and the capacitor; and an epoxy resin molding film for molding the piezoelectric device, the capacitor and the lead frame into a unitized form. The high frequency resonator further includes: a plurality of electrodes formed by printing a metal paste on one face of a sub-wafer of a capacitor chip, the plurality of the electrodes being interconnected by a plurality of connection electrodes; and a second plurality of electrodes formed by printing a metal paste on another face of the sub-wafer, the plurality of the electrodes being interconnected by a plurality of connection electrodes with a same connection structure.
In still another aspect of the present invention, the method for manufacturing a ceramic resonator according to the present invention includes the steps of: forming a ceramic piezoelectric device, a capacitor chip and a lead frame; assembling the piezoelectric device and the capacitor chip into the lead frame; and molding the assembled chip by using epoxy resin. The process for making the capacitor includes the steps of: cutting a ceramic wafer into a plurality of sub-wafers; printing a plurality of electrodes on one face of the sub-wafer in addition to connection electrodes; drying the sub-wafer thus printed; printing a second plurality of electrodes on another face of the sub-wafer in addition to connection electrodes; drying the second plurality of the electrodes; baking the sub-wafer thus dried; and cutting the sub-wafer thus baked into a plurality of capacitors.